In the human body, the epidural space is a narrow channel, located in and extending the length of the spine. FIGS. 1A and 1B illustrate, diagrammatically, the generally crescent shape cross-section of the epidural space 10 and its position within the spinal column 8. The epidural space 10 is defined along one edge or side by the dura mater 12 which surrounds the spinal cord 18. The epidural space is further defined along a second edge or side by the periosteum of the bony vertabrae or by the ligamentum-flavum 14 at the vertabral interspaces. Along the interior surface of the periosteum of the bony vertebrae or of the ligamentum-flavum 14 lies the venus plexis 19, a complex configuration of veins. Web-like fibrosis 20 may adhere to the dura mater 12 and the periosteum of the bony vertebrae and/or the ligamentum-flavum 14 in a random manner or in layers which form lesions extending across the epidural space 10 or parallel thereto. The fibrosis comprising an epidural lesion may have a consistency ranging from very soft to tougher, scar-tissue. An epidural lesion may extend through the epidural space over the length of two or three vertebrae. Such lesions are believed to be a source of lower back pain and possibly sciatica in human beings. These lesions are believed to be caused primarily by post operative scarring of nerves, particularly from laminectomy procedures. A ruptured disc or a leaking disc, caused by an annular tear, also are believed to be causes of epidural lesions.
Epidural lesions may be treated by surgical exploration. Unfortunately, such surgical exploration is difficult, time-consuming and often results in a painful post-operative recovery. Epidural lesions also have been removed by a method known as fluid lysis. In fluid lysis, an epidural catheter, typically comprising a flexible tubular shaft having an open distal end, is introduced between the vertebrae of the spinal column into the epidural space. The distal end of the epidural catheter is positioned adjacent the fibrosis comprising the lesion. A large volume of fluid is delivered through the catheter and directed against the fibrosis with enough force to break the web-like layers comprising the lesion. Unfortunately, fluid lysis may be ineffective because the fluid takes the path of least resistance upon leaving the distal end of the catheter, and often fails to impact the fibrosis with enough force to destroy the lesion. Consequently the lesion may not be completely removed and the procedure must be repeated.
Therefore it is among the general objects of the present invention to provide an improved method of treating fibrous lesions in the epidural space which avoids the foregoing and other difficulties.
In procedures, such as fluid lysis, which require introducing a catheter into the epidural space, it has long been standard practice to use a hollow metal needle having a knife-like distal tip, such as a Touhy or Huber needle, to penetrate the tough fibrous tissues surrounding the epidural space. The columnar strength and collapse resistance of the metal needle overcomes the resistance of the ligamentum-flavum and assists in maintaining the angle and position of the needle in the epidural space while the catheter is introduced into the epidural space through the needle. Although proper positioning of a catheter in the epidural space often requires advancing and retracting the catheter through the distal tip of the needle introducer. Unfortunately, the knife-like distal tip of the needle introducer is likely to damage and even shear off the catheter as the catheter is retracted possibly resulting in a severed portion of the catheter remaining in the epidural space. Difficult, complex surgery is necessary to retrieve such a severed portion from the epidural space. To avoid such a result, anesthesiologists traditionally have been taught never to withdraw or pull back a catheter through the metal needle introducer. Traditionally, positioning occurs by withdrawal of the catheter and the introducer needle simultaneously, with the positions of the two relative to one another remaining unchanged. Such a technique often results in multiple punctures before the catheter is positioned as desired in the epidural space.
More recently, in order to enable retraction of the epidural catheter, catheters having metal spring-like wire coverings have been introduced into the epidural space using Huber-type needles, in which the needle lumen opens at an angle with respect to the axis of the needle. The metal spring-like covering is less likely to be severed and may allow for limited reciprocating motion of the catheter through the needle introducer during positioning of the catheter. Although the risk of shearing such a spring reinforced catheter is not as high as with a conventional catheter, the risk of damaging the catheter still is very high.
The use of metal needle introducers has further discouraged the insertion into the epidural space of other medical devices, such as flexible fiberscopes and microsurgical instruments, because of the same risks associated with catheters.
Therefore it also is among the general objects of the invention to provide a catheter introducer for placing a catheter or other medical devices in the epidural space which avoids the foregoing and other difficulties.